1. Field of the Invention:
The present invention is directed to a method and device for sequentially recording holograms containing analogue or digital data into parallel extending tracks on a storage tape and to a method of retrieving the information.
2. Prior Art:
Presently known approaches for sequential optical data storage arrange for a time-variable signal to be modulated onto a laser beam by pulse amplitude modulation to provide an object beam is directed on a photo sensitive storage medium along with a constant (in time) coherent reference wave to produce interference patterns which are recorded as unidimensional or one-dimensional holograms on the moving tape.
Each modulated pulse corresponds to a hologram whose contrast is a measure of the amplitude of the corresponding modulated pulse.
Another approach, which is disclosed in U.S. Pat. application Ser. No. 290,796 which was filed on Sept. 21, 1972, and which issued as U.S. Pat. No. 3,805,275 on Apr. 16, 1974, utilized noncoherent light for sequential optical data storage. In this approach, a pulse amplitude modulated light beam is utilized to form unidimensional or onedimensional holograms in several parallel tracks on a storage tape, However, in this approach, a corrective illumination beam, which is physically and chronologically separate, must be used to insure that the overall illumination of the storage tape remains constant with each recording.
Between the incidence of two successive light pulses, the storage medium moves onward by a distance or interval .DELTA. x. The magnitude of this interval .DELTA. x depends upon the tape feed speed which in turn depends upon the band width of the signal being recorded. While it is desirable to store the individual holograms as close together as possible for example to arrange for the interval .DELTA. x to be at a minimum, the magnitude of the interval .DELTA. x cannot be made arbitrarily small.